Research Of Low-density-change Phase Change Memory Based On Ge-Sb Alloy

Phase-change memory(PCM)is considered as one of the most promising candidates for next-generation memory due to the large resistance contrast between amorphous and crystalline phases,fast switching,low power consumption and scalability.3D stacking technology such as 3D X-Point develops rapidly to realize high-density storage,promoting the development of PCM industry.However,the obvious mass density difference between the two phases leads to large volume change during phase transition,and the generated stress has a bad influence on the contact between phase change material and electrode,resulting in poor cycle performance of PCM.These problems become rather serious for high-density PCM,for the reason that the stress is more likely to influence the neighboring cells.To solve the problem,we choose carbon as the dopant into Ge-Sb alloy to reduce the density change(??)in this study.Compared to commonly used phase change materials such as GST,Ge-Sb stands out for its faster crystallization speed,higher phase-change temperature(Tc)and smaller ?? due to the absence of vacancy in the crystalline state.In our study,the ?? of Ge-Sb is further reduced by carbon doping,which renders GeSbC material an outstanding candidate for durable PCM devices.In this study,we deposit a series of GeSbC films with different carbon contents by magnetron sputtering firstly,and X-ray reflectivity and Atomic force microscopy measurement results show that smaller ??(3.29%)can be achieved when carbon content is 5.75 at.%,which is benefit for improving the working life of PCMs.In-situ temperature dependence of electrical resistivity testing result proves doping carbon into Ge-Sb can increase the Tc so that can improve the data retention ability.Besides,we fabricate lateral nanostructured PCMs based on GeSbC and test its electrical property.However,the results show that the electrical property is unstable and varies from cell to cell,and the reason may be fabrication error or phase separation of Ge-Sb.Finally,we reveal the role that carbon atom plays in the structure and properties of GeSbC alloy by experimental characterization and ab initio calculation.Through X-ray diffraction and X-ray photoelectron spectroscopy measurement,we can know that the GeSbC crystal has a rhombohedral structure similar to Sb,and C atoms have bonded with Ge and Sb atoms.Ab initio calculation reveals that C atoms prefer to form shorter tetrahedral bonds in the amorphous phase of GeSbC,slightly increasing the packing efficiency in the bonding areas,so that smaller ?? can be achieved.